W. B. Emery— Igneous Geology of Carrizo Mountain. 351 



sion, though all evidence of 

 possible outflows has been com- 

 pletely removed by erosion. 

 The relation of the igneous 

 rock and the surrounding sedi- 

 mentary beds which range from 

 Triassicto Upper Cretaceous in 

 age is shown on the accom- 

 panying map (tig. 1). 



Major intrusion. — The major 

 intrusion which has produced 

 the marked upturning of the 

 surrounding sedimentary beds 

 is only poorly exposed. There 

 are a number of large outcrops 

 but they are isolated and not 

 traceable, the one into the 

 other, because of the covering 

 of sediments. Consequently 

 the nature of the intrusion is 

 with difficulty ascertained. In- 

 deed, from the appearance of 

 the outcrops, which are in 

 many places very steep-walled, 

 it would seem that there was 

 not one large intrusion but sev- 

 eral smaller ones which had 

 united to produce a single re- 

 sult, — domal uplift. There is 

 no reason to doubt that whether 

 of one large intrusion or sev- 

 eral smaller ones, the outcrops 

 represent a single period of 

 igneous activity, and that the 

 inagmacame from one common 

 reservoir. 



Sills ancl sheets. — On the 

 north of the mountain and dip- 

 ping from it at an angle of 

 about 15° is an intrusion of sill- 

 like form entirely confined 

 within the base of the Upper 

 Jurassic (?) sediments. This 

 sill, which has been called the 

 Tisnasbas sill, from the canyon 

 of that name where it is best 

 exposed, is somewhat thicker 

 at its innermost margin, where 

 it is seen in connection with 



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